linux-kernel - Re: [RFC 19/19] s390/facilities: enable AP facilities needed by guest

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Message-Id: <40cdab64-9eeb-02bd-f260-80e9da8c9034@linux.vnet.ibm.com>
Date:   Thu, 2 Nov 2017 14:49:12 -0400
From:   Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>, freude@...ibm.com
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, heiko.carstens@...ibm.com, cohuck@...hat.com,
        kwankhede@...dia.com, bjsdjshi@...ux.vnet.ibm.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pmorel@...ux.vnet.ibm.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, qemu-s390x@...gnu.org,
        jjherne@...ux.vnet.ibm.com, thuth@...hat.com,
        pasic@...ux.vnet.ibm.com
Subject: Re: [RFC 19/19] s390/facilities: enable AP facilities needed by guest

On 11/02/2017 11:53 AM, Christian Borntraeger wrote:
>
> On 11/02/2017 04:36 PM, Tony Krowiak wrote:
>> On 11/02/2017 08:08 AM, Christian Borntraeger wrote:
>>> On 10/16/2017 11:25 AM, Martin Schwidefsky wrote:
>>>> On Fri, 13 Oct 2017 13:39:04 -0400
>>>> Tony Krowiak <akrowiak@...ux.vnet.ibm.com> wrote:
>>>>
>>>>> Sets up the following facilities bits to enable the specified AP
>>>>> facilities for the guest VM:
>>>>>      * STFLE.12: Enables the AP Query Configuration Information
>>>>>                  facility. The AP bus running in the guest uses
>>>>>                  the information returned from this instruction
>>>>>                  to configure AP adapters and domains for the
>>>>>                  guest machine.
>>>>>      * STFLE.15: Indicates the AP facilities test is available.
>>>>>                  The AP bus running in the guest uses the
>>>>>                  information.
>>>>>
>>>>> Signed-off-by: Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
>>>>> ---
>>>>>   arch/s390/tools/gen_facilities.c |    2 ++
>>>>>   1 files changed, 2 insertions(+), 0 deletions(-)
>>>>>
>>>>> diff --git a/arch/s390/tools/gen_facilities.c b/arch/s390/tools/gen_facilities.c
>>>>> index 70dd8f1..eeaa7db 100644
>>>>> --- a/arch/s390/tools/gen_facilities.c
>>>>> +++ b/arch/s390/tools/gen_facilities.c
>>>>> @@ -74,8 +74,10 @@ struct facility_def {
>>>>>   			8,  /* enhanced-DAT 1 */
>>>>>   			9,  /* sense-running-status */
>>>>>   			10, /* conditional sske */
>>>>> +			12, /* AP query configuration */
>>>>>   			13, /* ipte-range */
>>>>>   			14, /* nonquiescing key-setting */
>>>>> +			15, /* AP special-command facility */
>>>>>   			73, /* transactional execution */
>>>>>   			75, /* access-exception-fetch/store indication */
>>>>>   			76, /* msa extension 3 */
>>>> With this all KVM guests will always have the AP instructions available, no?
>>>> In principles I like this approach, but it differs from the way z/VM does things,
>>>> there the guest will get an exception if it tries to execute an AP instruction
>>>> if there are no AP devices assigned to the guest. I wonder if there is a reason
>>>> why z/VM does it the way it does.
>>> A good question. For LPAR it seems that you have AP instructions even if you have
>>> no crypto cards.
>>>
>> I don't believe these facilities control whether or not AP instructions will be available
>>
>> to the guest.
> This is actually handled by your patch2 enabling the ECA bit.
> I think we must decide if we want to be able to disable these instructions
> via the cpu model. If yes we must then couple the facilities with the enablement.
The ECA.28 bit controls whether instructions are intercepted or 
interpreted - i.e., handled via hardware
virtualization. If set, as is done in patch2, then instructions will be 
interpreted. I don't see how
that affects enabling or disabling AP instructions, unless we don't set 
ECA.28, intercept every instruction
and program check. Am I missing something here?
>